Production of articles of improved water resistance from urea-formaldehyde resins



Patented Sept. 15, 1953 UNITED STATES PATENT OFFICE PRODUCTION OF ARTICLES OF IMPROVED WATER RESISTANCE FROM UREA-FORM- ALDEHYDE RESINS No Drawing.

Application March 8, 1951,

Serial No. 214,634

4 Claims.

The invention relates to the production of articles of greatly improved water resistance from urea-formaldehyde resins.

Articles molded from melamine-formaldehyde molding compositions and laminates prepared from melamine-formaldehyde resins have substantially greater water resistance than similar materials prepared from urea-formaldehyde products. However, melamine is considerably more expensive than urea so that melamineformaldehyde products are more expensive than urea-formaldehyde products. Therefore, it has been necessary to use urea-formaldehyde materials in many applications for which the water resistance of urea-formaldehyde materials is not wholly satisfactory, but for which the cost of melamine-formaldehyde materials is too great.

Furthermore, melamine-formaldehyde compositions produce molded articles of inferior appearance (due to inherent yellow color and lack of translucency) which makes it impossible to use such compositions in certain applications for which high water resistance is desirable. For example, urea-formaldehyde buttons have been used in many cases in which melamine-formaldehyde buttons have been considered unacceptable because of their yellow color and their dead (opaque) appearance, in spite of the relatively poor resistance to laundering of urea-formaldehyde buttons.

The principal object of the invention is the production of articles of greatly improved water resistance from urea-formaldehyde resins. More specific objects and advantages are apparent from the description, which illustrates and discloses but is not intended. to limit the invention.

Attempts have been made heretofore to produce molding compositions having the good qualities of both ureaand mela1nine-formaldehyde compositions by the use of combinations'of urea and melamine. However, it has been found that substituting urea for some of the melamine used to produce a melamine-formaldehyde composition produces a disproportionate reduction in the water resistance and other qualities of articles formaldehyde molding composition by substituting melamine for part of the urea used.

The present invention is based upon the disor laminate prepared from the untreated cellulose filler. Although it has been found that a disproportionately small improvement is produced by merely substituting melamine for part of the urea used in producing a urea-formaldehyde molding composition, the use of the same proportion of melamine in accordance with the method of the present invention produces a disproportionately large improvement.

The remarkable improvement obtained in the practice of the present invention has been demonstrated as follows:

A cellulose filler impregnated with a thermosetting reaction product of formaldehyde and melamine was prepared by the following procedure: A reaction mixture consisting of melamine (57 grams) in formalin (110 grams of a 37 per cent commercial aqueous formaldehyde solution) was held for five minutes at temperatures ranging from 90 to 95 C. (The terms "per cent and parts" as used herein refer to per cent and parts by weight unless otherwise specifled.) The resulting reaction mass was diluted with water to a volume of 1000 cc. Lactic acid (0.5 cc. of a 10 per cent solution) was added to adjust the pH to a range between 5 and. 6. The resulting solution was then used to impregnate alpha cellulose (558 grams of which 6 per cent was water). The resulting impregnated filler was cured for three hours at a temperature of about 220 F. to yield a coarse, granular popcornlike material. The dried popcorn (415 grams) Was further impregnated with a mixture of (1) a urea-formaldehyde reaction product solution (1170 grams); prepared by maintaining a solution of urea (390 grams) in formalin (790 grams of a commercial 37 per cent aqueous formaldehyde solution) at a temperature of about 30 C. and a pl-I' of 7 for six hours) and (2) lactic acid (2 cc; of a 10 percent solution). The impregnated material was dried for approximately minutes so obtained Was dried at a temperature of about 185 F. for two hours, and theneurediet atom.-

4 A, 1, 2, 3, 4 and minutes) in a mold heated by 75 pounds steam to produce small disks suitable for testing water resistance. The water resistance of a disk molded from each composition :fpr each period of cure was measured by immersing it in boiling water for minutes. The results obtained for each test piece are shown in Table 1 below, as the gain in weight perature of about 224)" F. for three hours;

then at a temperature of about 200 for, an additional 16 hours. The completely dry popcorn (415 grams) was further impregnated with a rriixtureof a urea-forma1dehyde reaction product (i n .,grams) during immersion. (Water resistance, .of ecourseynaries with the amount of moisture-that an article is capable of absorbing because the degree of deterioration upon exposure to moisture varies-with the amount of moisture absorbed After the water absorption determination, each'test piece was dried for four days at. a temperature of about F. The condition oj finch test piece after the drying operation is indicated directly below the Water absorption results as OK (unaflected), s1. or. (slightly cracked), v. sl. cr. very slightly cracked) or or. (cracked) TABLE 1 Water AbsorptionTCure time..(min.) Moldmg .r. oomposi Resmougdgggction .finer m v m V A v v V tion $14 I 1 2V 3 7 4 5 A Urea-,formaldehyde Melamine-formaldehydeirn- {,1 1 5 .095 .090 085 (185 pregnated' cellulose. -v. -51. er. OK 0 K O K O K OK' B "EN-J10 af t el l lfl fi lmprpg- 21 or gl or or 51 or O Melamine-Urea-forcelluloseQn lQn: 1 5 '.1 9('l' I 1 35"" llifi' L" li'o 1n dehyde. or. or. ;sl.cr -v.s1.cr er. 'cr. Urea-frag e]dehyiie .,.,do l7 5 ,129 .150 ,155 l 5 5 er. or. or. or. cr. er.

solution prepared as .hfireinhefore described (-1170 grams) and lactic aeid1('3;.-5 cc; of 10 per cent solution) The impregnated material so obtained was dried at-a tempe atureoi about 135 grees F. for 35 minutes andwas then ground-ma ball mill with the ,sameba'llmill additivesused inpreparing composition A, to obtaili a cgntrol 11191.61- ing composition, B,

A solution of melamine (37.9,grams) ip-jormalin 87 rams of a :37 pe ent ceinlmercie aqueous formaldehyde s 1 time) --w as heldata temperature of about 189 for 10 minutes to produce .a solution of a mela ne-iprmaldeh-yde reaction product. This solution wasthen mixed with a solution of a urea-formaldehyde r action product prepared as hereinbetoredeseribed 1170 grams) and the resultin urea-rnflarnine resin solution along with lactic acid (8.5 cc. of a '10 per cent solution) was absorbed on alpha cellulose (373 grams) of which finer-cent was-water). The impregnated material so, btained was dried at a temperature of aboutn degreesF. for F10 minutes, and was then ground. ina ball mill together with the ball-mill additivesillt ljpinbefore described to obtain a second control molding composition, C.

A solution of a urea-formaldehyde reaction product (1300 grams) prepared as hereinbefore described, along with lactic acid (5.5- cc. of a 10 per cent solution) was absorbed 9,1 alpha cellulose (37.3 grams of which .6 per cent was water). The material so obtained was dried at a temperature of about 1 85 degrees F; for" 40 minutes, and the dried material was ground in ball mill together with :the ball mil'l additives hereinbefore described :to obtain a third control molding composition, -D.

Compositions A, and D were molded under one to four tons of pressure per square inch of p oje ed area for Various periods o t me n I impregn ted with a ur efo m l e yd re e ie product, control B. Nor is the present improvem n m-the' W t es tance o u ea-f r d h e meld-ins coms on sl me b usin p imar fil e but ubs t in ma i amount of a mela-mineefor-maldehyde reaction product -for-part of thelurea formaldehyde reaction product, qnt 'ql fli h em t pr melam neier d h dere e i n equ l s d i con em esitio fl s t e Same esthe hrq ti n. u e o imp eg a e a cel ul s fi le i the ompos iQ -Q the in en en A .A he resu t ieTeble 1 also n icate the cemp tion of t ein nt e s w ons dera greater resistance tocrack-ing upon subjection to extreme changes of temperature and humidity than any of the three control compositions, B, C and -D.

' To demonstrate further the superiority of articles molded from compositions of the instant n n i n, empos t A of the n i n and con ro empesitign D were used omo s tumbler f r t cal tum ler c ck n te talider tum l s 6- a, tumb ers 4 in h h hha in a bot om diameter. of 2 /4 inchesend a topd ameter of 3 nches were meld d hetweenthe lates of a 20 ton hydraulic press and then were tested as follows:

In each cycle of the test the tumblers were filled with water and were placed in a vented oven that was maintained at a temperature of about 140 F., for a total time of 24 hours. The test, therefore, provided an accelerated fractureproducing effect of water evaporating from a molded article in an atmosphere of warm air. at the end of each cycle of this test the tumblers had been throughly dried and thoroughly emptied. of their contents by evaporation.

A tumbler molded from composition A of the invention showed no cracking after cycles of the above procedure. However, a tumbler molded from control composition D was badly cracked after only 7 cycles. It is apparent from these results that molding compositions of the invention produce molded articles of greater heat re sistance and of greater water-resistance than articles produced from urea-formaldehyde molding compositions comprising an ordinary cellulose filler.

The method of the present invention, which produces a material that can be hot-pressed to produce articles of greatly improved water resistance, comprises impregnating cellulose with a thermosetting reaction product of formaldehyde and a substance whose molecule has a plurality of NH2 groups each connected to a carbon atom contained in a heterocyclic ring, the carbon atom being connected by a double bond to an intracyclic nitrogen atom, converting the,

reaction product to its infusible state, and then impregnating the cellulose with a thermosetting urea-formaldehyde reaction product.

Cellulose When the material produced by the present method is a molding composition of the invention, various forms of cellulose may be used as the filler to be impregnated with a resinous reaction Heterocyclic poZyamine-formcldehzjde reaction product For the sake of brevity. a substance whose molecule has a plurality of NH? groups each connected to a carbon atom contained in a heterocyclic ring, said carbon atom being connected by a double bond to an intracyclic nitrogen atom, is hereinafter referred to as a heterocyclic poly amine.

A. heterocyclic polyarnine that maybe reacted Alpha with formaldehyde to form a thermosetting reacplurality of NH2 groups each attached to a nu-;.

clear carbon atom in a triazole ring, such as guanazole,

NH5C=N NHi i-phenyl guanazole NHzC=N l-guanyl guanazole NHZ o=N NH l-acetyl guanazole l E Q (b) a substance whose molecule contains a plurality of NH2 groups each attached to a nuclear carbon atom in a diazine ring, e. g.,' a pyrimidine such as 2,4-diamino-6-hydroxy pyrimidine,

ore-o HO-C /N or a quinazoline such as 2,4-diaminoquinazoline,

or (c) a substance whose molecule contains a plurality of NH2 groups each attached to a nuclear carbon atom in a triazine ring, having from one to three triazine rings, and having no'functional groups attached to a triazine ring other than the amino groups (such as an amino triazine). The term functional group as used herein means any radical in a molecule of such a substance which may enter into undesirable side reactions that interfere with the reaction of formaldehyde with the amino triazine in the production of compositions of theinvention (e. a. an OH group attached to a triazine. ring. may react with formaldehyde during the production of a thermosetting amino triazine-formaldehyde condensation product).

Such a substance may-be a triamino triazine, e. g., melamine,

or a diamino triazine (i. e., a monoguanamine) having the general formula wherein R is a hydrogen atom, a saturated monovalent aliphatic hydrocarbon radical having from 1 to 18 carbon atoms, anaromatiohydrocarbon radical containing 1 benzene nucleus or containing 2 condensed benzene nuclei, a saturated or unsaturated cycloaliphatic hydrocarbon radical, or any of the foregoing radicals containing substituents such as aliphatic, cycloaliphatic, aromatic, alkoxy, aryloxy and .acyl radicals. Thus, the monoguanamines used may have varying structures and may be of complex structure so long as they do not contain groups which interfere with the condensation reaction of forma1de-- hyde with the guanamine in the practice of the invention. Such monoguanamines include,

Formoguanamine,

NH: 110/ \N Acetoguanamine,

/NH: N-C

, HaC--C /N NET Propioguanamine,

NH: Ho-cHPo N "Butyroguanamine,

NH: N-O/ Hac 'cHr cflr C /N' N=Ci Benzoguanaminc.

Ph nyla toguanaminc,

Delta-eyano-valeroguanamine,

NEa

and monoguanamines Obtained from the corresponding mononitriles containing as many as 1 carbon atoms, e. g., dodecano-, tetradecano-, or octadecano-nitrile. A substance whose molecule containsv a plurality of NH2 groups (as hereinbefore described) may also be a diguananiine having the general formula wherein R is a divalent hydrocarbon radical in which the shortest connection between the free valences is not more than eighteen carbon atoms in series and which contains no substituents or contains substituents such as aliphatic, cycloaliphatic, aromatic, alkox-y, aryloxy'and acy-l radicals, or may be a compound having said general formula that is substitutedon not more than two exocyclicv nitrogen atoms, the substituents consisting of (a) not more than two monovalent aliphatic hydrocarbon radicals on each substituted nitrogen atom, each having. not more than four carbon atoms, each having at least one hydrogen atom attached to the same carbon atom as the free valence, and each having not more than one unsaturation, any such unsaturation being an olefinic unsaturation in the beta-gamma position, (b) not more than one monovalent radical of the benzene series on each substituted nitrogen atom having notmore than eight carbon atoms in which the free valence is connected to the nucleus, and (c) not more than one monoalkoxy phenyl radical on each substituted nitrogen atom having not more than eight carbon atoms. Thus the diguanamines used may have varying structures and may be of complex structure so long as they donot contain groups which interfere with the condensation reaction of formaldehyde with the diguanamine in the practice of the invention. Such diguanamines include gamma-,methyl-gamma-acetyl pimeloguanamine,

' NH: 7 NH:

Adipoguanamine,

Bis-(4,6-diamino-2-triazinyl-ethy1) iiuorene,

H2NC

Phthaloguanamine,

1,2bis-2,4-diamino-6-triazinyl naphthalene,

sym. diphenylsebacoguanamine, sym. di pphenetyladipoguanamine, sym.-di-o-tolyladipoguanamine, terephthaloguanamine and diguanamine obtained from nitriles such as 2,4-dicyanodiphenyl, 4,4 dicyanodiphenyl methane, 4,4-dicyanodiphenyl ethane, and 4,4dicyano alpha,gamma-diphenyl propane. The polyguanamines which may be used in the practice of the invention include trlguanamines such as gamma- 2,4diamino-6-triaziny1-gamma phenylpimeloguanamine.

A guanamine which contains one or a plurality of 2,4-diamino-6-triazinyl radicals (e. g., a monoguanamine, diguanamine or triguanamine) may be prepared by condensing the corresponding mononitrile, dinitrile or trinitrile with dicyanidiamide. The nitrile which reacts with the dicyandiamide must be a specific type of nitrile, namely, a nitrile whose molecule contains a cyano radical attached to a saturated carbon atom. In other words, the carbon atom to which the cyano group is attached must not be unsaturated and must not become unsaturated under the reaction conditions. In a nitrile used in a reaction with dicyandiamide as described herein, a nuclear carbon atom in an aromatic ring structure (e. g., an atom in a benzene nucleus) is considered to be saturated.

A mononitrile or polynitrile which may be used in the preparation of a guananiine for use in the present invention may be the nitrile corresponding to a monocarboxylic acid or a polycarboxylic acid, for example, any normal aliphatic carboxylic acid in the series from acetic acid to octadecanoic acid, or in the series from malonic acid to octadecane 1,18-dicarboxylic acid, any benzene carboxylic acid, or an aromatic carboxylic acid containing two condensed benzene nuclei or two benzene nuclei connected directly or connected by from one to twelve atoms in series, a saturated or unsaturated alicylic carboxylic acid, the dimer of linoleic acid, or an acid obtained by substituting in the molecule of any of the foregoing acids substituents such as aliphatic, cycloaliphatic, aromatic, alkoxy, aryloxy and acyl radicals. Examples of such nitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, stearonitrile, succinonitrile, glutaronitrile, pimelonitrile, adiponitrile, sebaconitrile, azelaonitrile, octadecanedinitrile, benzonitrile, phthalonitrile, terephthalonitrile, cyanonaphthalene, dicyancphthalene, 2,4-dicyanodiphenyl, 4,4'-dicyanodiphenyl methane, 4,4'-dicyanodiphenyl, 4,4'-dicyanocliphenyl ethane, 4,4 dicyanoalphagamma diphenyl propane, 4,4-dicyanodiphenyl ether, 4.- cyanophenyl i-cyanobenzyl ether, 4,4'--dicyanodibenzyl ether, the ethers formed by the reaction of two molecules of a hydroxy benzonitrile (e. g., 4-hydroxy benzonitrile) with one molecule of the dibromide corresponding to a glycol in the series from methylene gylcol to decylene glycol or to diethylene or triethylene glycol, gamma-methylgamma-acetylpimelonitrile, gamma-isopropenylgamma-acetylpimelonitrile, bis-cyanoethyl fluo- '11 rene, 4,4-dicyanobenzophenone, phenylacet'oni trile, gamma-cyano-gamma--phenylpimelonitrile and the dinitrile corresponding to the dimer of linoleic acid.

In the preparation of a guanamine by the condensation of a nitrile with dicyandiamide, widely different molal proportions may be used. How"- ever, in the preparation of a monogu'an'amine the preferred proportion ranges from about 1 mol to about 1.5 mols of dicyandiamide for each mol'of the nitrile (preferable a mononitril'e) and the best results are obtained when the molal proportion is about 1.2 mols of di'cyandiamide for each mol of the nitrile. In the preparation of a diguanamine the preferred proportion ranges from about 2.2 to about 2.6 mols of dicyandiamide for each mol of the nitrile (i. e., a dinitrile) and the best results are obtained by using about 2.4 mols of dicyandiamide for each mol of the nitrile. correspondingly, in the preparation of a triguanamine the preferred proportion of dicyandiamide is slightly greater than 3 mols (i. e., about 3.6 mols) fori'each moi of the nitrile '(i. e., a trinitrile).

The condensation of a nitrile with di'cy-andiamide is carried out by dissolving a strongly basic catalyst in a suitable primary or secondary alcoholic solvent such as benzyl alcohol or ethylene glycol mono-methyl ether, adding the nitrile and the dioyandiamide in a proportion within the range hereinbefore described, and heating to start the reaction. The reaction is then continued by heating'or cooling if necessary to keep the temperature between about 100 and about 180 C. and to prevent the reaction from becoming too violent. The quantity of the alcoholic solvent used should be just sufficient to form a suspension of the precipitate that can be stirred during the reaction. When the precipitation of the guanamine is complete, the precipitate is filtered off and washed with boiling water to: remove excess dicyandiamide and products of side reactions. The guanamine may be purified by converting it to a hydrochloride and neutralizing an aqueous solution of the hydrochloride to liberate the guanamine.

This method of preparation is versatile-in that a large variety of nitriles may be used for the reaction with di'cyandiamide, to give a wide variety of guanamines.

The nitriles may be prepared by various methods. Dinitriles in which the cyano groups are separated by five carbon atoms in series, and in which the central carbon atom of the series is disubstituted, may be prepared by condensing acrylonitrile and a compound having an active methylene group, in the presence of a strong base. Other dinitriles may be prepared'by'reacting a polymethylene dihalide with sodium cyanide. Often it is convenient to prepare the nitrile by dehydration ofthe amide or directly from the carboxylic acid.

Diguanamines in which one or two of the execyclic nitrogen atoms are substituted, as, for -example, sym.-diphenyladipoguanam-ine, hereinbefore mentioned, may be prepared by various methods. One method consists in reacting l-phenyl biguanide, l-o-tolyl biguanide, l-mtolyl biguanide, l-p-tolyl biguanide, '1-(2,5-di'- methyl phenyl) biguanide, l-methyl-el-p-henylbiguanide, l-p-phenetyl bigua'nide or l-et-hyl-l phenyl biguanide with sodium carbonate and adipyl chloride or the dichloride ofany other dicarboxylic acid in chlorobenzene. Another method consists in reacting any of the aforementioned aryl or alkyl aryl biguanides or I-methyl biguanide, l-ethyl biguanide, l-propyl biguanide, 1- butyl-biguanide, l-allyl biguanide, l-crotyl biguanide, 1,1-dimethyl biguanide, 1,1-diethyl biguanide or 1,l-diallyl biguanide, with the diethyl or dimethyl ester of adipic acid or any other dicarboxylic acid in the presence of an alkoxide catalyst. Still another method consists in reacting an alkyl or aryl dicyandiamide such as phenyl dicyandiamide with adiponitrile or the dinitrile of any other dicarboxylic acid.

A thermosetting hetero-cyclic polyamine-formaldehyde reaction product may be obtained by reacting a heterooyclic polyamin'e, as hereinbee fore defined (or a mixture of such amines), either with formaldehyde or with a polymer thereof, such as paraformaldehyde. When used for this reaction, paraformaldehyde is considered to split up so that the substance actually taking part in the reaction is formaldehyde. The heterocyclic polyamine may be reacted with a solution of formaldehyde in water, in an organic solvent such as an alcohol, or in a liquid containing both water and an organic solvent. A water solution is usually preferred because it swells the cellulose, permitting a more efficient impregnation by the resinous reaction product. The reaction may be performed in an autoclave, if desired, to secure a reaction temperature above the boiling point of the solvent. The heterocyclic polyami-ne may be added to an ordinary commercialaqueous formaldehyde solution having a pH of about 4, or to such a solution which has been made less acid, or neutral, or alkaline, preferably at a pH between 6 and 8, by addition of any desired base, such as sodium hydroxide, ammonium hydroxide, borax, or triethanolamine.

In general, the proportion of formaldehyde actually reacting may range from one-half to a maximum of two molecules for each amino group. An excess of formaldehyde above this maximum may be used for the reaction if desired, although an uncombinable excess of one of the reactants usually is not desirable in the final product. Because of the complexity of the molecules of the reaction products that are produced, the proportion of formaldehyde actually reacting may vary freely between the limits stated. The preferred proportions vary, of course, with the specific substance that is reacted with formaldehyde. For example, when the substance is melamine, the preferred proportions are about 3 mols of formaldehyde for each mol of melamine. Other examples of preferred molar ratios of formaldehyde to a heterocyolic polyamine in the preparation of a resinous reaction product for the impregnation of a cellulose filler in the practice of the invention are 2:1 for guanazole or l-carbamyl guanazole, 4:1for 2,4-diamino-6-hydroxy pyrimidine, 3:1 for 2,4-diamine quinazoline, 251 for formoguanamine, acetoguanamine or benzoguanamine and 5:1 for adipoguanamine or sebacoguanamine.

The reaction proceeds at normal temperatures, but heating ordinarily is desirable to shorten the time of reaction, or, in some cases, to dissolve the substanc to be reacted with formaldehyde. The desired resin solution ordinarily is obtained by carrying the reaction only to its earliest stage, for example, the stage at which the reacting iiigredients have just dissolved to form a solution, or for a few additional minutes thereafter.

When the reaction between formaldehyde and a heterooyclic polyamine is substantially complete, the solution of th reaction product is used to impregnate cellulose by the procedure hereinafter described. The preferred heterocyclic polyamine in the practice of the invention is melamine, since melamine-formaldehyde resin-treated cellulose imparts superior properties to molding compositions and laminating materials in the practice of the invention.

Preparation of resin-treated cellulose fillers For the sake of brevity, a cellulose filler which has been impregnated with a thermosetting reaction product of formaldehyde and a heterocyclic polyamine is hereinafter referred to as a resin-treated filler. In the preparation of a resin-treated filler, a heterocyclic polyamineformaldehyde reaction product solution, prepared as hereinbefore described, is diluted with water or any suitable solvent so that the weight of the diluted solution is from two to three times the weight of the cellulose to be treated. (The weight of the cellulose is always taken as its bone dry weight. The cellulose employed need not be bone dry, of course, so long as its water content is accounted for in calculating its weight.) The dilution should be made carefully so that the resin does not precipitate as the water is added. It is desirable that the pH of the resin solution be adjusted (e. g., with dilute lactic acid) so that it is on the slightly acid side, since the resin cures to its infusible state on the filler more rapidly in a slightly acid condition. (The preferred pH varies in accordance with the particular heterocyclic polyamine-formaldehyde reaction product solution employed. Melamine-formaldehyde reaction product solutions are preferably used at a pH between and 6.)

When the reaction product has thoroughly impregnated the cellulose filler, it is essential that the material be thoroughly dried and that the resinous reaction product be cured on the filler to the infusible state. Although the slightly acid pH of the impregnating solution aids the cure initially, several hours of heating may be necessary at an elevated temperature to completely deaden the resinous substance. (Melamine-formaldehyde resins derived from solutions having a pH between 5 and 6 usually cure in about three hours at temperatures ranging from 200 to 225 F.) The completeness of cure may be checked from time to time during the curing operation by boiling a sample of the treated filler in water. If the cure is still incomplete, a cloudy solution will result because of dissolved resinous reaction product. On the other hand, if the solution is clear, complete cure is indicated.

The proportion of a heterocyclic polyamineformaldehyde reaction product solution used to impregnate a cellulose filler should be such that from 2.5 to 40 per cent of the final treated dry filler consists of the heterocyclic polyamineformaldehyde reaction product in its infusible state. It is preferred that the proportion of the reaction product solution be such that from about 14 to about 25 per cent of the final treated filler consists of the reaction product in its infusible state.

If the heterocyclic polyamine used is one that reacts so rapidly with formalin that the reaction product reaches the insoluble stage almost lm-- mediately after the reactants are mixed and heated (guanazole is an example of such a heterocyclic polyamine) it is preferable simply to mix the polyamine and the formalin at room temperature and then to add the water of dilution, and the acid to adjust the pH. The relatively clear solution so obtained is then absorbed on a cellulose filler, which is thoroughly dried in accordance with the procedure hereinbefore described. Thus, the reaction between the heterocyclic polyamine and the formaldehyde actually takes place on the cellulose filler during the drying operation. The preparation of a resin-treated cellulose filler on a commercial scale can be accomplished in a paper pulp manufacturing plant. When paper pulp is prepared, sheets of dry pulp can be passed through a bath of a heterocyclic polyamineformaldehyde reaction product and, after the resin absorption, the impregnated pulp sheets can be redried and rolled for shipment. Impregnation of the pulp in this manner would consist essentially of tub sizing the polyamine resin on the pulp while the pulp is being processed.

Preparation of molding compositions In the preparation of a molding composition of the invention by the present method a resintreated cellulose filler, prepared as hereinbefore described, is impregnated with a thermosetting urea-formaldehyde reaction product. The ureaformaldehyde reaction product may be prepared by reacting urea and formaldehyde in the preferred molar ratio of about two to three. A resin solution may be obtained by carrying the reaction only to its earliest stage, for example, the stage at which the reacting ingredients have just dissolved to form a solution, or by carrying the reaction to any further stage (short of the insoluble stage) By advancing the reaction, it is possible to obtain thermosetting urea-formaldehyde condensation products that are insoluble but still fusible. Such reaction products may be converted by heat into infusible resins. When the reaction is substantially complete, the resulting urea-formaldehyde resin is used to further impregnate a resin treated cellulose filler. It is usually preferable to render the resulting mixture acid (pH from about 4 to about 6). Heat may be used to facilitate the drying of the composition, but, of course, the drying temperature should not be suihcient to render a thermosetting molding composition infusible. The dry product may be ground in a ball mill to produce a homogeneous powder.

The proportions of urea-formaldehyde reaction product and resin-treated filler should be such that from about 20 to about 50 per cent of the final dry composition consists of resintreated filler. It is preferred that from about 25 to about 35 per cent of the final dry composition consist of resin-treated filler, since articles molded from such compositions have superior properties.

Any of the known methods may be employed to grind or powder the molding materials. When the material is ground in a ball mill the customary additives, for example, plate lubricants, plasticizers, and curing catalysts of various types, may be easily incorporated. The amount used in the case of each of such additives is the usual amount consistent with its particular function in the molding composition.

It is well recognized that articles molded from ordinary urea-formaldehyde molding compositions have greater translucency than articles molded from melamine-formaldehyde molding compositions.

The translucency of articles molded from a urea-formaldehyde composition of the invention which comprises a melamine -formaldehyde resin-impregnated cellulose filler is equally as good as the translucency of articles molded from ordinary urea-formaldehyde molding compositions. Dixon-r se, translucency is :a particular ,advantage .in. a plastic. when it is accompanied by good waterresistance. Itis frequently desired to manufacture. plastic articles, for example, buttons,.tha;t are translucent, colorful and water resistant so that they can undergo repeated launderings and still present a good appearance. While standard urea--formaldehyde articles possessgood color properties (i. e., they do not have the inherent yellow color of melamine-formaldehyde plastics) and also .possess a high degree of translucency, they are notsufficiently resistantto water to be useful in the manufacture of articles that. are subjected to frequent moisture and temperature variations for prolonged periods of time. Melamine-formaldehyde plastics have good water resistance, but ordinarily they possess a yellowish appearance which frequently hinders color blending and hinders their use in, for example, the manufacture of shirt buttons and other plastic articles which must have the whitest appearance possible.

Furthermore, the heat resistance of articles molded from compositions embodying the invention is as good as the'heat resistance of articles molded from standard urea-formaldehyde .molding compositions. Good heat resistance is valuable, of course, for articles which undergo prolonged and frequent exposure to extreme temperature 'changes,'e. g., articlessuch as lighting fixtures or stove hardware.

It has been, suggested that scrap from the molding of standard melamine-formaldehyde plastic might provide a'low-cost source of filler material. However, the cellulose present in such scrap is so thoroughly impregnated with the hardened melamine resin as to render the scrap, when powdered for use as a filler, practically non-absorbent for additional resinous reaction product. (A molding composition of the present invention may comprise as high as 80 per cent of a urea-formaldehyde resin and as low as per cent of a resin-treated filler.)

When melamine-formaldehyde mOldihg scrap is ground or powdered'for use as an impregnated filler in a molding composition, plastic articles molded therefrom are of poor quality, crack easily, and, in general, present an inferior appearance. On the other hand, compositions of the invention produced from melamine. .resinimpregnated filler in accordance with the present method, inwhich the proportion of melamine resin is considerably less than that present in compositions which comprise ground scraps of melamine-formaldehyde plastic as a filler, possess superior physical properties as demonstrated herein.

Molding compositions of the invention produced by the present method have unusually good properties because they combine nearly all.

of the good qualities inherent inv both standard urea-formaldehyde and melamine-formaldehyde compositions, and yet do not contain so much melamine as to be uneconomical to produce. It has been shown hereinbefore that compositions embodying the invention not only possess excellent water resistance, a property earnestly de-- sired for plastic materials, but also possess other similarly good physical properties.

Using the procedure hereinbefore described for the preparation of a molding composition of the invention (A), three melamine-formaldehyde resin-treated cellulose fillers were prepared and then impregnated with a urea-formaldehyde reaction product in such proportions as to yield materials having the percentage compositions,

shown below:

A control molding composition, hereinafter referred to as composition 4, comprising 35 per cent of ordinary alpha cellulose and 65 per cent of a urea-formaldehyde reaction product (prepared according to the procedure hereinbefore described) was tested along with compositions l, 2, and 3 embodying the invention for strength properties and shrinkage.

The strength tests employed were standard tests for plastic materials and are considered to be capable of showing generally the strength characteristics that are important in industrial plastic materials. A separate description of the procedure used .in each test follows:

Fleacural strength (col. 2) .-A small bar 4" x x 6"), molded of the material to b tested for three minutes under a pressure of 5,000 lbs. per square inch in a mold heated with steam at 60 lbs. gauge pressure, is supported at its extremities and a transverse load is applied centrally. The fiexural strength 5 is the extreme fiber stress in pounds per square inch at which the bar fails, calculated according to the formula 3wl 2ba in which 10 is the load in pounds, I is the length in inches of the bar or span between the supports, 1) is the horizontal dimension in inches of the cross section of the bar and a is the vertical dimension in inches of the-cross section of the bar.

Deflection (col. 3).The deflection of the bar used in the flexural strength test is measured at the instant the bar'fails. The elastic modulus (in flexure) may be calculated from Youngs formula in which M is the modulus in pounds per square inch, my (mass times gravity) is the load in pounds, Z is the length in inches of the bar or span between supports, 8 is the deflection in inches, 00" is the vertical dimension in inches of the cross section of the bar and b is the horizontal dimension in inches of the cross section of the bar.

Compressive strength (col. 4) .--A small bar x X 1 molded under the same conditions'is subjected to a compressive force acting. longitudinally until the bar crumbles or shatters. The compressive strength is the force F in pounds per square inch at which. the bar fails, calculated according to the formula Moreover, shrinkage tests for articles molded from compositions of the invention indicate that shrinkage properties are greatly improved in such articles. Shrinkage is the reduction in .size of a molded article during cooling after molding, and the reduction in size during the useful life of the molded article. The contraction of a plastic upon being removed from the mold is called initial shrinkage, this contraction of the plastic occurring, of course, upon cooling to room temperature. Final shrinkage is the shrinkage due to the evaporation of any water present within a plastic article, upon exposure of the article to the atmosphere for a prolonged period of time. To hasten the loss of this water, test samples are suspended above concentrated H2804 in an atmosphere maintained at 90 F. The test is run for three weeks. Samples of compositions 1, 2, 3 and 4 were molded into disks having a diameter of two inches, by the procedure hereinbefore described, and were tested for initial and final shrinkage. The results are recorded in Table 2 as inches of shrinkage per inch of the molded article before testing.

The results of the shrinkage tests for the compositions of the invention are appreciably better than the shrinkage results for a standard ureaformaldehyde plastic. Compositions of the invention produce articles having substantially better shrinkage resistance. Good shrinkage properties are desirable, because reduced shrinkage lengthens the useful life of a molded article by minimizing the tendency toward cracking of the plastic article.

It has been shown that articlesmolded from compositions of the invention not only possess much better water resistance than standard urea-formaldehyde plastics, but also possess other properties which are at least as good and often much better than the corresponding properties of standard urea-formaldehyde plastics.

The advantageous properties of articles molded from compositions of the invention can be demonstrated by other tests. For example, plastic buttons, which are among the many com-'- mercially valuable plastic articles molded from compositions of the invention, can be tested by a button laundering test. In ordinary laundering, buttons are subjected to relatively hot alkaline solutions and then are subjected to fairly cold rinse water. Poor water resistance in the case of articles such as buttons results in cracked and warped buttons, or buttons having a generally poor appearance after several cycles of ordinary laundering. The superior water resistance of articles molded from compositions embodying the invention is illustrated by the button laundering test and also by the cosmetic jar lid test which are described below.

The button laundering test is essentially a test to determine the durability and water resistance of molded plastic articles (e. g., clothing buttons) that are frequently contacted by alkaline or acidic solutions. To compare molding compositions heretofore known with molding compositions of the instant invention, several suiting buttons were molded from the composition of the invention hereinbefore described as composition .2, the urea-formaldehyde control composition D,

and a melamine-formaldehyde control composition E, in a standard mens suiting button mold. The buttons obtained were sewn onto a hand towel, and ten suiting buttons and two overcoat buttons molded from each composition were used for the test.

The melamine-formaldehyde control composition E was prepared as follows: A reaction mixture of melamine (126 grams), formalin (243 grams of a commercial 3'7 per cent aqueous formaldehyde solution) and triethanolamine (1 cc. of a 50 per cent aqueous solution) was heated with stirring to a temperature of about 80 C. This temperature was maintained for a total time of about 15 minutes. When the melamine had dissolved, the pH of the syrup was about 6.8. The reaction mixture was then cooled to a temperature of about 60 C., and the cooled syrup then was absorbed on alpha cellulose (115 grams bone dry weight). The impregnated material so obtained was dried in a circulating air oven at a temperature of about 170 F. for a total time of about one hour. The crisp, friable dried material was ground in a ball mill together with 0.1 per cent of hexamethylene tetramine, 0.125 per cent of o-sulfamido methyl benzoate, 1.0 per cent of toluene sulfonamide as a lasticizer, and 0.5 per cent of zinc stearate as a plate lubricant. The resulting powder was used to mold buttons as hereinbefore described for the button laundering test. g

A cycle of the standard button laundering test used herein was begun by immersing and slushing each towel in an aqueous solution containing 0.1% of sodium carbonate and 0.2% of laundry soap maintained at a temperature of about F., for a total time of about 10 minutes. Subsequently the towel was immersed and slushed in an aqueous solution containing 0.2% of sodium carbonate and 0.4% of laundry soap at a temperature of about F. for a total time of 10 minutes. After this treatment the towel was rinsed in cold water for three minutes before being slushed in a 0.5% aqueous solution of acetic acid maintained at a temperature of about 110 F., for a total time of five minutes. The acetic acid treatment was followed by another rinse in cold water for a total time of three minutes, and then the towel was finally hung to dry at room temperature for 24 hours to complete the cycle. The buttons were examined after each cycle of this test, and the number of buttons remaining uncracked after the number of cycles indicated is recorded in Table 3 below. i

TABLE 3 Control Composition D Control Composition E Compo- The results of the button laundering test rer9 coriid in Table 3 indicate sat there is sub-stantiallil rfo difi'eience in resistance to laundering Between Molded co'in-pos itiofis embodyin the invention ahd the more ex ensive inela lnine formaldehyde m'old'ed Campos-Mons which have been kIlOWh heretofore -to have superior resistance to laundering. w

cosmetic jar lid test iar-finer demonstrates the superior water resistance of plastics embodythe the msta'nt invention. J-ar lids, each three inches in diameter, were 'molded at a temper t me of about 305" I. from the ih'oldin'g compositrons er the invehfiibh hereinuefcre referred to as "compositions -2 'ahd 3 and from tire c'ontrol composition D. The test lids were filled with boiling water and were allowed to stand for 10 minutes. the were then emptied, dried, and placed in a E. oven for 24 hours. This procedure 'co'nsfifiite'd a cycle which 'Wai's repeated uhtil the surface of the jar l-id "cracked.

jCompsition's 2 and *3 of the invention sustittiii'ed. 10 wees "of the'above procedure without cracking, whereas an ordinary urea-formaldehyde "molding composition ("control D) was badl'Y cracked after only three cycles.

Although the cempositions of the invent-mnemga'ldyed in the tests herfnbefore described comprise 'ine'l'am-ih -for lnal'deliyde resin-treated ceiii-rlos'e filler'sficenrpesitions comprising other heteroeyelic polyamine-foimaldehyde resin-treated teueiose fillers also have good chemical and physical properties, as demonstrated below' v ((t) A suspension of adiD'Ogu'anar'nine (-36.8 g rams) in ior r'nalin (64. 8 grams of a commercial 3-? ber *crit a'qeeus formaldehyde solemn) was diluted with water (406 grams) and ethylene glycol 'mondmetnyiemer (1 grams) and was refluxed for about '20 minutes, at a temperature "of about 100 C. until a clear water-soluble resin was obtained having a. pH of approximately 61-8. '-"1'-hereactioh product so f'o'rin'ed was a'bsorbed on cellulose (308 grams bone dry), the pH of the mixture being adjusted to about 4 to by the audit-1mm la'ctic acid ('8 bf 10% solution). The impregnated 'filler so obtained was then baked for "six days at a temperature of about 190 to completely -"ci-1ie the resinous reaction product on the cellulose. A

(19) -A soli1tibn' of'giiariazole 49.5 gra'i'ris) in water "("665 grams) was prepared. Fo'r'ma'l-m (8 1 of a cornirier'cial 3 per cent atfiieoiis rermalue wae-soieeom was aiddedfto th'e Elia-Ila zole solution and e pH was adjusted to just 'b'elow 6 by the addition-0f mbue acid. The resiilting "soliitwnwas absorbed tn cellulose (401.5 giarhs, bone dry). The impregnated filler was then dried'fo'r five days at'a terniatn're tr atom "190" F. to completely cure 'the "resintsiis reaction product thereon.

Each treated fill er prepared as described 'infa) and (6) above was further a impregnated with a solution of a urea-formaldehyde reaction product, prepared as hereinbefore described, and the impregnated material 'was thoroughly dried and ground into a powdered molding composition, "by the procedure he'reinbefore described. --In each case the ipr'oportion o'f treated filler and of ureatormaldehyde resin solution wa such that the final dry molding composition comprised 40 .per "cent of the treated filler and 60 percent of the urea-formaldehyde reaction product. The com- Tposition containing the adipoguaiiamirieforn'ialdehyde resin-treated filler is hereinafter referred to as composition 5 and the compositioncontain- 2'6 7 the gua r'xazole-fo'rmaldehyde resin r is hereinafter referred to as edmpesitioi-i *6. (The adrpogua emme-gfermamhyde resin ate the guarlaz'ole r'r'haldefiyde 'i esi'ncomprised 1655 per cent of the treated fillers.)

The com etition (if the i-flVIitidil hieii'lbbfflre seem-thee as composition 2, which comprises a Water AbsorptionMolding time in minutes Molding composition v 0.170 0.150 0.145 for. 'c'r.

-0.-1-15 01085 0.080 V 3 s1. or. ,v. s1. or v. v,v.s1.cr 0.150 '11 0.110 1 sLc'r. I vA'sLcr 6 {0. 145 o. 0. 100 0. 095 s1.er. slscr. fs1.cr. S1. or

:As the results in Table 4 indicate, a ureait-or'r'r naldehyde molding composition of the invention which comprises a cellulose filler impregnated with a thermosetting reaction product of formaldehyde and melamine (2),brf61inaldehyde and adipoguafnaminea (5), or formalde hyde aind guahazole (6) can. be molded to'pr'oduce articles having considerably higher water resistance than 'a urea-formaldehyde molding c'dmpbsitidn chcom'pris's an oruifiar 'cefiw lose filler, con 01D. The ccsfiipcsitionstr the intention also show "considerably greater 'resii'stance "to cracking u't'on subjection to extreme cha' es of 'terfip'ei'attireahd humidity than the 'coii elcompesitidn. Itisalsoevidentfrofil the rsl'fltsih Table "4 that a "composition the Ve'htion which cbffiprisesa "mmminarqrmamehyde treated filler has even better properties 'a composition'of the invention in which the hate'rocyclic polyaniine which is reacted with farmaldehyde comprises, rer example, adipogdan airline or guan'azole. p e

It has been demonstrated that "iioldirig compositions embodying the invention are superior to standard urea-formaldehyde plastics. Furthermore, the superior water resistance and heat resistance of melamine-romaidehyde plastics and the superior color qualities, jt'ranslucency, and strength properties "or area-formaldehyde plastics areconibined in melting c'oinposition's'o'f the invention"; yet "coiripdsitions of the invention can "be producedfnearly as'econoinically as stand-'- ard ure'a -formaldel'iyde plastics.

Preparation of laminates A laminating material '-"may be prepared by a procedure similar to that -hereinbefore described for the preparation of a molding ecsmpdsiaen es:- cept, -'0 "f course, that the cl-liilosedngredie'rit consists of 's-beets df-'celliilosic 'materia1 (e. g., p'a i)er or cloth) The cellulose sheets are fii'st impregnated with 19, heteroeycl'i'c polyaniine formaldehyde reaction product, and the reaction :product is completely cured before the cellulose sheets are coated with the binder (i. e., a urea-formaldehyde reaction product, as hereinbefore described), prior to a hot-pressing operation in accordance with the usual procedure for producing laminates.

In the preferred method of preparing impregnated cellulose sheets for use in a laminate embodying the invention, a cellulose cloth or paper is dipped in a solution of a heterocyclic polyamine formaldehyde reaction product and then dried, preferably at an elevated temperature, in order to convert the reaction product to the infusible state. It may be desirable to use a cellulose cloth which includes other fibers such as glass or asbestos interwoven with the cellulose fibers. As a practical matters in an industrial application, pulp in a paper machine may be pretreated by the manufacturer so as to produce paper sheets already impregnated with a substantially infusible reaction product. Other methods of impregnating cellulose laminating materials, such as spraying or brushing an aqueous or organic solvent solution of the intermediate reaction product onto the material, may also be employed.

It is preferred that the proportion of a hetero cyclic polyamine-formaldehyde reaction product solution used to impregnate the cellulose sheets be such that about 10 to 20 per cent of the final treated dry cellulose sheets consists of the heterocyclic polyamine-formaldehyde reaction product in its infusible state.

The proportion of urea-formaldehyde reaction product to resin-treated plies should be such that approximately 40 to 60 per cent of the final cured laminate consists of the resin-treated cellulose plies.

The following examples illustrate the practice of the invention:

EXAMPLE 1 A reaction mixture of a heterocyclic polyamine (67.5 grams of melamine) and formalin (130 grams) is reacted for five minutes at a temperature ranging from 90 to 95 C. The resulting reaction mass is then diluted with water to 1000 cc. and the pH is adjusted to about 5 to 6 by the addition of lactic acid (0.5 cc. of a per cent lactic acid solution). The solution of the reaction product is absorbed on alpha cellulose (337.5 grams, bone dry weight) and the resulting material is dried for several hours at a temperature of about 200 to 220 F. The dried filler (450 grams) is then impregnated with a solution of a urea-formaldehyde reaction product (550 grams), prepared by reacting a solution of urea (372 grams) and formalin (752 grams) at a temperature of about 30 C. and at a pH of about 7 for about six hours. The material so obtained is dried for approximately one hour at a temperature of about 185 F. Subsequently the dried material is ground in a ball mill with 0.1 per cent of hexamethylene tetramine, 0.25 per cent of ethylene glycol toluene sulfonate as an accelerator, 1.0 per cent of toluene sulfonamide as a plasticizer, and 0.5 per cent of zinc stearate as a plate lubricant, to obtain a powdered molding composition of the invention, which can be molded into articles having superior water resistance, resistance to shrinkage, etc.

within about 3 minutes.

22 EXAMPLE 2 A reaction mixture of a heterocyclic polyamine (47.7 grams of benzoguanamine) and formalin (48.6 grams) is heated to the boiling point to dissolve substantially all of the benzoguanamine The hot solution is diluted with methanol (250 grams) and Water (311 grams) to obtain a clear solution. Lactic acid is added to adjust the pH to approximately 4 to 5. This solution is absorbed on alpha cellulose (334 grams, bone dry weight) and the resulting product is dried and cured for seven days at a temperature of about 190 F.

The resulting dried impregnated filler (400 grams) is further impregnated with a solution of urea-formaldehyde reaction product (600 grams), prepared by reacting a solution of urea (405 grams) and formalin (908 grams) for six hours at a temperature of about 30 C. and at a pH of about 7. The product so obtained is dried for approximately one hour at a temperature of about C. and is then ground in a ball mill with 0.1 per cent of hexamethylene tetramine, 0.25 per cent of ethylene glycol toluene sulfonate as an accelerator, 1.0 per cent of toluene sulfonamide as a plasticizer, and 0.5 per cent of zinc stearate as a plate lubricant. The resulting powdered composition may be molded into articles having good water resistance and very good resistance to shrinkage.

Having described the invention we claim:

1. A method of producing a material that can be hot pressed to produce articles of greatly improved water resistance, which comprises impregnating cellulose with a thermosetting reaction product of formaldehyde and a substance Whose molecule has a plurality of NH2 groups each connected to a carbon atom contained in a heterocyclic ring, the ring consisting of from five to six carbon and nitrogen atoms of which not more than three are nitrogen atoms, the carbon atom being connected by a double bond to an intracyclic nitrogen atom, converting the reaction product to its infusible state, the amount of the reaction product being such that 2.5 to 40 per cent of the treated cellulose consists of the infusible reaction product, and then thoroughly impregnating the cellulose with an aqueous solution of a thermosetting urea-formaldehyde reaction product, and drying.

2. A method as claimed in claim 1 wherein the substance is melamine.

3. A molding composition that gives molded articles of greatly improved water resistance, pre-, pared by the method of claim 2.

4. A molding composition that gives molded articles of greatly improved water resistance, prepared by the method of claim 1.

DAVID E. CORDIER. WILLIAM D. WILLIAMS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,280,934 Seebach Apr. 28, 1942 2,411,554 Riccitiello Nov. 26, 1946 2,542,484 Debing Feb. 20, 1951 

1. A METHOD OF PRODUCING A MATERIAL THAT CAN BE HOT PRESSED TO PRODUCE ARTICLES OF GREATLY IMPROVED WATER RESISTANCE, WHICH COMPRISES IMPREGNATING CELLULOSE WITH A THERMOSETTING REACTION PRODUCT OF FORMALDEHYDE AND A SUBSTANCE WHOSE MOLECULE HAS A PLURALITY OF NH2 GROUPS EACH CONNECTED TO A CARBON ATOM CONTAINED IN A HETEROCYCLIC RING, THE RING CONSISTING OF FROM FIVE TO SIX CARBON AND NITROGEN ATOMS OF WHICH NOT MORE THAN THREE ARE NITROGEN ATOMS, THE CARBON ATOM BEING CONNECTED BY A DOUBLE BOND TO AN INTRACYCLIC NITROGEN ATOM, CONVERTING THE REACTION PRODUCT TO ITS INFUSIBLE STATE, THE AMOUNT OF THE REACTION PRODUCT BEING SUCH THAT 2.5 TO 40 PER CENT OF THE TREATED CELLULOSE CONSISTS OF THE INFUSIBLE REACTION PRODUCT, AND THEN THOROUGHLY IMPREGNATING THE CELLULOSE WITH AN AQUEOUS SOLUTION OF A THERMOSETTING UREA-FORMALDEHYDE REACTION PRODUCT, AND DRYING. 